Stent grafts for use in human or animal vasculature, such as in the aorta of a patient, are known and where such stent grafts are to be placed in the region of a vessel which has a side branch, it is known to have fenestrations to allow blood flow into the side branch vessel from the stent graft.
There have been proposals for an internal leg on such a stent graft so that an auxiliary branch vessel can be extended from the main stent graft to seal in the internal leg and extend through the fenestration to the side branch vessel.
Throughout this specification the term distal with respect to a portion of the aorta, a deployment device or a prosthesis is the end of the aorta, deployment device or prosthesis further away in the direction of blood flow away from the heart and the term proximal means the portion of the aorta, deployment device or end of the prosthesis nearer to the heart. When applied to other vessels similar terms such as caudal and cranial should be understood.